The better you feel, the more comprehensible it is (7)

I believe the answer is:

braille

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'it is' is the definition.
The definition suggests a singular noun which matches the answer.

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(Other definitions for braille that I've seen before include "Print language for blind" , "System of writing for the visually-impaired" , "Points raised" , "Raised text for the blind" , "Language read by touch" .)

I've seen this clue in the Evening Standard.

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